Abstract

The objectives of this investigation are to determine the major transportation paths for the Recent beach sands of the Gulf of Mexico and to relate the textures and mineralogy of the Recent sands to their depositional environments. Approximately 200 Recent sand samples were collected from the rivers and beaches of the Gulf Coast states. Mechanical analyses were made to determine the grain size and sorting. Spectrochemical methods were used to determine chemical composition, and thin-section Rosiwal analyses were used to determine mineralogical composition. The major conclusions of this investigation are as follows: 1) The Recent beach sands E. of the Mississippi River delta are mature quartz sands which contain practically no feldspar and a mature heavy-mineral suite rich in staurolite and kyanite. The Recent beach sands W. of the Mississippi River are feldspathic. The feldspar abundance of these sands decreases from the Mississippi delta area westward in the direction of prevailing longshore currents, mainly by dilution. The heavy-mineral suite of the Recent beach sands from Louisiana and E. Texas contains abundant unstable minerals; among the resistant heavy minerals, garnet predominates over staurolite and kyanite. 2) The relative abundance of unstable heavy minerals which can easily be decomposed during weathering or by postdepositional changes is not a reliable criterion for paleogeographic interpretations. On the other hand, feldspar abundance and ratio of garnet to staurolite plus kyanite, can be used to recognize ancient petrologic provinces.

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